Light-emitting aluminum gallium indium nitride compound semiconductor device having an improved luminous intensity

ABSTRACT

A light-emitting semiconductor device ( 10 ) consecutively includes a sapphire substrate ( 1 ), an AlN buffer layer ( 2 ), a silicon (Si) doped GaN n + -layer ( 3 ) of high carrier (n-type) concentration, a Si-doped (Al x3 Ga 1-x3 ) y3 In 1-y3 N n + -layer ( 4 ) of high carrier (n-type) concentration, a zinc (Zn) and Si-doped (Al x2 Ga 1-x2 ) y2 In 1-y2 N emission layer ( 5 ), and a Mg-doped (Al x1 Ga 1-x1 ) y1 In 1-y1 N p-layer ( 6 ). The AlN layer ( 2 ) has a 500 Å thickness. The GaN n + -layer ( 3 ) has about a 2.0 μm thickness and a 2×10 18 /cm 3  electron concentration. The n + -layer ( 4 ) has about a 2.0 μm thickness and a 2×10 18 /cm 3  electron concentration. The emission layer ( 5 ) has about a 0.5 μm thickness. The p-layer  6  has about a 1.0 μm thickness and a 2×10 17 /cm 3  hole concentration. Nickel electrodes ( 7, 8 ) are connected to the p-layer ( 6 ) and n + -layer ( 4 ), respectively. A groove ( 9 ) electrically insulates the electrodes ( 7, 8 ). The composition ratio of Al, Ga, and In in each of the layers ( 4, 5, 6 ) is selected to meet the lattice constant of GaN in the n + -layer ( 3 ). The LED ( 10 ) is designed to improve luminous intensity and to obtain purer blue color.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the invention

[0002] The present invention relates to a light-emitting semiconductordevice that emits blue light and uses a group III nitrogen compound.

[0003] 2. Description of the Prior Art

[0004] It has been known that an aluminum gallium indium nitride(AlGaInN) compound semiconductor may be used to obtain a light-emittingdiode (LED) which emits blue light. This semiconductor device is usefulbecause of its high luminous efficiency resulting from direct electrontransition and because of its ability to emit blue light, which is oneof the three primary colors.

[0005] Irradiating an electron beam into an i-layer to which magnesium(Mg) is doped and heat treatment is carried out enables the i-layer tohave a p-type layer of the AlGaInN semiconductor device. As a result, aLED with a double hetero p-n junction structure includes an aluminumgallium nitride (AlGaN) p-layer, a zinc (Zn) doped indium galliumnitride (InGaN) emission layer and an AlGaN n-layer, becomes usefulinstead of a conventional LED of metal insulator semiconductor (MIS)structure which includes an n-layer and a semi-insulating i-layer.

[0006] The conventional LED with a double hetero p-n junction structureis doped with Zn as an emission center. Luminous intensity of this typeof LED has been improved fairly. Still, there exists a problem inluminous efficiency and further improvement is necessary.

[0007] The emission mechanism of a LED with an emission layer doped withonly Zn, or only an acceptor impurity, as the emission center iselectron transition between conduction band and acceptor energy levels.However, a large difference of their energy levels makes recombinationof electrons through deep levels dominant which deep level recombinationdoes not contribute to emission. This results in lower luminousintensity. Further, the wavelength of light from the conventional LED isabout 380 to 440 nm, or shorter than that of pure blue light.

[0008] Further, the emission layer doped with Zn as the emission centerexhibits semi-insulative characteristics. Its emission mechanism isexplained by recombination of an electron through acceptor levelinjected from an n-layer and a hole injected from a p-layer. However,the diffusion length of the hole is shorter than that of the electron.It results in high ratio of holes disappearing in a non-emission processbefore recombination of the hole and electron occurs in the emissionlayer. This phenomenon impedes higher luminous intensity.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to solve the aboveproblem and improve the luminous intensity of the LED of AlGaInNsemiconductor, or obtain enough spectrum to emit a purer blue light.

[0010] According to the first aspect of the invention, there is provideda light-emitting semiconductor device comprising:

[0011] an n-layer with n-type conduction of group III nitride compoundsemiconductor satisfying the formula Al_(x3)Ga_(y3)In_(1-x3-y3)N,inclusive of x3=0, y3=0 and x3=y3=0,

[0012] a p-layer with p-type conduction of group III nitride compoundsemiconductor satisfying the formula Al_(x1)Ga_(y1)In_(1-x1-y1)N,inclusive of x1=0, y1=0 and x1=y1=0,

[0013] an emission layer of group III nitride compound semiconductorsatisfying the formula Al_(x2)Ga_(y2)In_(1-x2-y2)N, inclusive of x2=0,y2=0 and x2=y2=0;

[0014] the junction layer of the n-layer, the p-layer, and the emissionlayer being any one of a homo-junction structure, a singlehetero-junction structure, and a double hetero-junction structure; and

[0015] wherein the emission layer is formed between the n-layer and thep-layer, and doped with both a donor and an acceptor impurity.

[0016] It is preferable that the donor impurity is one of the group IVelements and that the acceptor impurity is one of the group II elements.

[0017] Preferable combinations of a donor and an acceptor impurityinclude silicon (Si) and cadmium (Cd), silicon (Si) and zinc (Zn), andsilicon (Si) and magnesium (Mg), respectively.

[0018] The emission layer can be controlled to exhibit any one of n-typeconduction, semi-insulative, and p-type conduction depending on theconcentration ratio of a donor impurity and an acceptor impurity dopedthereto.

[0019] Further, the donor impurity can be one of the group VI elements.

[0020] Further, it is desirable to design the composition ratio of Al,Ga, and In in the n-layer, p-layer, and emission layer to meet each ofthe lattice constants of the three layers to an n⁺-layer of high carrierconcentration on which the three layers are formed.

[0021] Further, a double hetero-structure sandwiching of the emissionlayer of p-type conduction by the n-layer and p-layer improves luminousefficiency. Making the concentration of acceptor impurity larger thanthat of the donor impurity and processing by electron irradiation orheat treatment changes the emission layer to exhibit p-type conduction.Magnesium, an acceptor impurity, is especially efficient for obtainingp-type conduction.

[0022] Further, doping any combinations of the described acceptor anddonor impurity to an emission layer of p-type conduction also improvesluminous efficiency. The luminous mechanism doped with acceptor anddonor impurities is due to recombination of an electron at donor leveland a hole at the acceptor level. This recombination occurs within theemission layer, so that luminous intensity is improved.

[0023] Further, a double hetero-junction structure of a triple-layersandwiching the emission layer having a narrower bad gap by the n-layerand p-layer having a wider band gap improves luminous intensity. Sincethe emission layer and the p-layer exhibit p-type conduction, valencebands of those layers are successive even without applying externalvoltage. Consequently, holes readily highly exist within the emissionlayer. In contrast, conduction bands of the n-layer and the emissionlayer are not successive without applying an external voltage. Applyinga voltage enables the conduction bands to be successive and electrons tobe injected deeper into the emission layer. Consequently, the number ofinjected electrons into the emission layer increases ensuringrecombination with holes and a consequent improvement in luminousintensity.

[0024] Other objects, features, and characteristics of the presentinvention will become apparent upon consideration of the followingdescription in the appended claims with reference to the accompanyingdrawings, all of which form a part of the specification, and whereinreferenced numerals designate corresponding parts in the variousfigures.

BRIEF DESCRIPTION OF THE DRAWING

[0025] In the accompanying drawings:

[0026]FIG. 1 is a diagram showing the structure of the LED embodied inExample 1;

[0027]FIGS. 2 through 7 are sectional views illustrating successivesteps of producing the LED embodied in Example 1;

[0028]FIG. 8 is a diagram showing the structure of the LED embodied inExample 2;

[0029]FIG. 9 is a diagram showing the structure of the LED embodied inExample 3;

[0030]FIG. 10 is a diagram showing the structure of the LED embodied inExample 4;

[0031]FIG. 11 is a diagram showing the structure of the LED embodied inExample 5;

[0032]FIGS. 12 and 13 are diagrams showing the structure of the LEDembodied in Example 6;

[0033]FIG. 14 is a diagram showing the structure of the LED embodied inExample 7; and

[0034]FIGS. 15 and 16 are diagrams showing the structure of the LEDembodied in Example 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0035] The invention will be more fully understood by reference to thefollowing examples.

EXAMPLE 1

[0036]FIG. 1 shows a LED 10 embodied in Example 1. It has a sapphire(Al₂O₃) substrate I upon which the following five layers areconsecutively formed: an AlN buffer layer 2; a silicon (Si) doped GaNn⁺-layer 3 of high carrier (n-type) concentration; a Si-doped(Al_(x2)Ga_(1-x2))_(y2)In_(1-y2)N n⁺-layer 4 of high carrier (n-type)concentration; a cadmium (Cd) and Si-doped(Al_(x1)Ga_(1-x1))_(y1)In_(1-y1)N emission layer 5; and a Mg-doped(Al_(x2)Ga_(1-x2))_(y2)In_(1-y2)N p-layer 6. The AlN layer 2 has 500 Åthickness. The GaN n⁺-layer 3 is about 2.0 μm in thickness and has a2×10¹⁸/cm³ electron concentration. The n⁺-layer 4 is about 2.0 μm inthickness and has a 2×10¹⁸/cm³ electron concentration. The emissionlayer 5 is about 0.5 μm in thickness. The i-layer 6 is about 1.0 μm inthickness and has a 2×10¹⁷/cm³ hole concentration. Nickel electrodes 7and 8 are connected to the p-layer 6 and the n⁺-layer 4, respectively.They are electrically insulated by a groove 9.

[0037] The LED 10 is produced by gaseous phase growth, called metalorganic vapor phase epitaxy referred to as MOVPE hereinafter.

[0038] The gases employed in this process are ammonia (NH₃), a carriergas (H₂ or N₂), trimethyl gallium (Ga(CH₃)₃) (TMG hereinafter),trimethyl aluminum (Al(CH₃)₃) (TMA hereinafter), trimethyl indium(In(CH₃)₃) (TMI hereinafter), dimethylcadmium ((Cd(CH₃)₂) (DMCdhereinafter), silane (SiH₄), diethylzinc ((C₂H₅)₂Zn) (DEZ hereinafter)and biscyclopentadienyl magnesium (Mg(C₅H₅)₂) (CP₂Mg hereinafter).

[0039] The single crystalline sapphire substrate 1, whose main surface‘a ’ was cleaned by an organic washing solvent and heat treatment, wasplaced on a susceptor in a reaction chamber for the MOVPE treatment.Then the sapphire substrate 1 was etched at 1100° C. by a vapor of H₂fed into the chamber at a flow rate of 2 liter/min. under normalpressure for a period of 5 min.

[0040] On the etched sapphire substrate 1, a 500 Å thick AlN bufferlayer 2 was epitaxially formed on the surface ‘a ’ under conditions oflowering the temperature in the chamber to 400° C., keeping thetemperature constant, and supplying H₂, NH₃ and TMA for a period ofabout 90 sec. at a flow rate of 20 liter/min., 10 liter/min., and1.8×10⁻⁵ mol/min., respectively. On the buffer layer 2, about a 2.2 μmthick Si-doped GaN n⁺-layer 3 of high carrier concentration with anelectron concentration of about 2×10¹⁸/cm³ was formed under conditionsof keeping the temperature of the sapphire substrate 1 at 1150° C. andsupplying H₂, NH₃, TMG, and diluted silane to 0.86 ppm by H₂ for thirtyminutes at a flow rate of 20 liter/min., 10 liter/min., 1.7×10⁻⁴mol/min. and 200 ml/min., respectively.

[0041] The following manufacturing process provides for an emissionlayer 5 as an active layer, an n⁺-layer 4 of high carrier concentration,and a p-layer 6 as a clad layer; the LED 10 is designed to emit at a 450nm wavelength peak in the luminous spectrum and have luminous centers ofCd and Si.

[0042] On the n⁺-layer 3, about a 0.5 μm thick Si-doped(Al_(0.47)Ga_(0.53))_(0.9)In_(0.1)N n⁺-layer 4 of high carrierconcentration with an electron concentration of 1×10¹⁸/cm³ was formedunder conditions of keeping the temperature of the sapphire substrate 1at 850° C. and supplying N₂ or H₂, NH₃, TMG, TMA, TMI, and dilutedsilane to 0.86 ppm by H₂ for 60 min. at a flow rate of 10 liter/min., 10liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min.and 10×10⁻⁹ mol/min., respectively.

[0043] On the n⁺-layer 4, about a 0.5 μm thick Cd andSi-doped(Al_(0.3)Ga_(0.7))_(0.94)In_(0.06)N emission layer 5 was formedunder conditions of keeping the temperature of the sapphire substrate 1at 850° C. and supplying N₂ or H₂, NH₃, TMG, TMA, TMI, DMCd, and dilutedsilane to 0.86 ppm by H₂ for 60 min. at a flow rate of 20 liter/min., 10liter/min., 1.53×10⁻⁴ mol/min., 0.02×10⁻⁴ mol/min., 2×10⁻⁷ mol/min. and10×10⁻⁹ mol/min., respectively. At this stage, the layer 5 exhibitedhigh resistivity. The impurity concentrations of the Cd and the Si dopedto the emission layer 5 were 5×10¹⁸/cm³ and 1×10¹⁸/cm³, respectively.

[0044] On the emission layer 5, about a 1.0 μm thick Mg-doped(Al_(0.47)Ga_(0.53))_(0.9)In_(0.1)N p-layer 6 was formed underconditions of keeping the temperature of the sapphire substrate 1 at1000° C. and supplying N₂ or H₂, NH₃, TMG, TMA, TMI, and CP₂Mg for 120min. at a flow rate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min.,0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min. and 2×10⁻⁴ mol/min., respectively.Resistivity of the p-layer 6 was 10 ⁸ Ω·cm or more exhibiting insulativecharacteristics. The impurity concentration of the Mg-doped into thep-layer 6 was 1×10²⁰/cm³.

[0045] Then, electron rays were uniformly irradiated into the p-layer 6using a reflective electron beam diffraction device. The irradiationconditions were set at 10 KV for the accelerating voltage, 1 μA for thesample current, 0.2 mm/sec. for the speed of the beam scanning, 60 μmφfor the beam aperture, and at 5.0×10⁻⁵ Torr vacuum. This irradiationchanged the insulative p-layer 6 into a p-type conductive semiconductorwith a hole concentration of 2×10¹⁷/cm³ and a resistivity of 2 Ω·cm.Thereby, a wafer with multi-structural layers was obtained as shown inFIG. 2.

[0046] The following FIGS. 3 to 7 show sectional views of an individualelement on the wafer. In actual practice and in accordance with industrycustom, a wafer with a large number of elements thereon is treated bythe following process and divided or diced into individual elements.

[0047] A 2000 Å thick SiO₂ layer 11 was formed on the p-layer 6 bysputtering. Then, the layer 11 was coated with a photoresist layer 12.Two selected parts or areas of the photoresist layer 12, named A and B,were removed by photolithography as shown in FIG. 3. The part or area Ais an electrode forming part which corresponds to a place where a hole15, shown in FIG. 5, is formed extending to and into the n⁻-layer 4 ofhigh carrier concentration. The part or area B corresponds to a placewhere a groove 9 shown in FIGS. 5 and 6 is formed for insulating orelectrically insulating the part or area A from an electrode in contactwith the p-layer 5.

[0048] As shown in FIG. 4, two parts of the SiO₂ layer 11 which were notcovered with the photoresist layer 12 were etched off by an etchingliquid such as hydrofluoric acid. Then, the exposed part of thefollowing successive three layers from the surface of the device, thep-layer 6, the emission layer 5, and the upper part of the n⁺-layer 4 ofhigh carrier concentration, were removed by dry etching, or supplying ahigh-frequency power density of 0.44 W/cm² and BCl₃ gas of 10 ml/min. ata vacuum degree of 0.04 Torr as shown in FIG. 5. After that, dry etchingwith argon (Ar) was carried out on the device. Consequently, a hole 15for forming an electrode reaching the n⁺-layer 4 of high carrierconcentration and a groove 9 for insulation are formed.

[0049] The SiO₂ layer 11 remaining on the p-layer 6 was removed byhydrofluoric acid as shown in FIG. 6. A nickel (Ni) layer 13 waslaminated on the entire surface of the device by vapor deposition. Thus,the so-formed Ni layer 13 in the hole 15 it in electrical contact withthe n⁺-layer 4 of high carrier concentration. A photoresist 14 wasdeposited on the Ni layer 13 and, then, was selectively etched off byphotolithography as shown in FIG. 7 leaving patterns of configurationfor electrodes connected to the n⁺-layer 4 of high carrier concentrationand the p-layer 6, respectively.

[0050] Using the photoresist 14 as a mask, the exposed part or area ofthe Ni layer 13 from the photoresist 14 was etched off by an etchingliquid such as nitric acid. At this time, the nickel layer 13 laminatedin the groove 9 was also removed completely. Then, the photoresist layer14 was removed by a photoresist removal liquid such as acetone. Therewere formed two electrodes, the electrode 8 for the n⁺-layer 4 of highcarrier concentration and the electrode 7 for the p-layer 6. A wafertreated with the above-mentioned process was divided or diced into eachelement which shows a gallium nitride light-emitting diode with a p-njunction structure as shown in FIG. 1.

[0051] The obtained LED 10 was found to have a luminous intensity of 100mcd and a wavelength of 450 nm by driving current of 20 mA.

[0052] The emission layer 5 preferably contains impurity concentrationsof Cd and Si within a range of 1×10¹⁷/cm³ to 1×10 ²/cm³, respectively,in order to improve luminous intensity. It is further desirable that theconcentration of Si is smaller than that of Cd by ten to fifty percent.

[0053] In order to make the band gap of the emission layer 5 smallerthan those of its respective adjacent two layers, i.e., the p-layer 6and the n⁺-layer 4 of high carrier concentration, a doublehetero-junction structure was utilized for the LED 10 in thisembodiment. Alternatively, a single hetero-junction structure can beutilized.

[0054] Further, it is preferable that the composition ratio of Al, Ga,and In in the respective three layers 4, 5, and 6 is selectivelydesigned to meet the lattice constants of their layers 4, 5, and 6 withthe lattice constant of GaN in the n⁺-layer 3 of high carrierconcentration as precisely as possible.

EXAMPLE 2

[0055]FIG. 8 shows a LED 10 utilized in Example 2. The emission layer 5in Example 1 was doped with Cd and Si. In this Example 2, an emissionlayer 5 is doped with Zn and Si.

[0056] A manufacturing process of a sapphire substrate 1, the formationof the AlN buffer layer 2 and the n⁺-layers 3 was similar to thatdiscussed in the previous example.

[0057] About a 0.5 μm thick Si-doped (Al_(0.3)Ga_(0.7))_(0.94)In_(0.06)Nn⁺-layer 4 of high carrier concentration with an electron concentrationof 2×10¹⁹/cm³ was formed on the n⁺-layer 3 under conditions of loweringthe temperature in the chamber to 800° C., keeping the temperatureconstant, and supplying N₂, NH₃, TMG, TMA, TMI, and diluted silane to0.86 ppm by H₂ for 120 min. at a flow rate of 20 liter/min., 10liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min.,and 10×10⁻⁹ mol/min., respectively.

[0058] About a 0.5 μm thick Si- and Zn-doped(Al_(0.09)Ga_(0.91))_(0.99)In_(0.01)N emission layer 5 was formed on then⁺-layer 4 under conditions of lowering the temperature in the chamberto 1150° C., keeping it constant, and supplying N₂, NH₃, TMG, TMA, TMI,diluted silane to 0.86 ppm by H₂, and DEZ for 7 min. at a flow rate of20 liter/min., 10 liter/min., 1.53×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min.,0.02×10⁻⁴ mol/min. and 10×10⁻⁹ mol/min., and 2×10⁻⁴ mol/min.,respectively. The impurity concentration of the Zn- and Si-doped intothe emission layer 5 was 2×10¹⁸/cm³ and 1×10¹⁸/cm³, respectively.

[0059] About a 1.0 μm thick Mg-doped (Al_(0.3)Ga_(0.7))_(0.94)In_(0.06)Np-layer 6 was formed on the emission layer 5 under conditions oflowering the temperature in the chamber to 1100° C., keeping thetemperature constant, and supplying N₂, NH₃, TMG, TMA, TMI, and CP₂Mg ata flow rate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min.,0.47×10⁻⁴ mol/min., 10.1×10⁻⁴ mol/min., and 2×10⁻⁴ mol/min.,respectively. The impurity concentration of Mg doped into the p-layer 6was 1×10²⁰/cm³. At this stage, the p-layer 6 remained insulative with aresistivity of 10⁸ Ω·cm or more.

[0060] Then, the p-layer 6 was processed to have p-type conduction byelectron beam irradiation under the same conditions described inExample 1. The subsequent process steps of forming the electrodes arethe same as that described in the previous example. The so-obtained LED10 was found to have a luminous intensity of 1000 mcd and a wavelengthof 450 nm by driving current of 20 mA.

EXAMPLE 3

[0061]FIG. 9 shows a structural view of a LED 10 embodied in Example 3.The LED 10 in Example 3 was manufactured by additionally doping Mg tothe emission layer 5 of the LED in Example 2. Other layers andelectrodes were manufactured in the same way as those in Example 2.

[0062] CP₂Mg was fed at a flow rate of 2×10⁻⁴ mol/min. into a chamber inaddition to the gasses employed in Example 2 in order to manufacture theemission layer 5 in Example 3. The emission layer 5 was about 0.5 μmthick comprising Mg, Zn, and Si-doped(Al_(0.09)Ga_(0.91))_(0.99)In_(0.01)N. Its resistivity was 10⁸ Ω·cmremaining insulative. Impurity concentration of Mg, Zn, and Si was1×10¹⁹/cm³, 2×10¹⁸/cm³, and 1×10¹⁸/cm³ respectively.

[0063] Then, both of the emission layer 5 and a p-layer 6 were subjectto electron beam irradiation with the electron beam diffraction deviceunder as same conditions as in Example 1. Thus, the emission layer 5 andthe p-layer 6 turned into layers exhibiting p-type conduction with ahole concentration of 2×10¹⁷/cm³ and resistivity of 2 Ω·cm.

EXAMPLE 4

[0064]FIG. 10 shows a structural view of a LED 10 embodied in Example 4.In this example, an emission layer 5 includes GaN and had a singlehetero-junction structure. Namely, one junction comprises a heavilySi-doped n+-layer 4 of high carrier concentration and a Zn- and Si-dopedGaN emission layer 5, and another junction includes the GaN emissionlayer 5 and a Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 with p-typeconduction. In this example, the Mg-doped GaN p-layer 62 as a contactlayer is formed on the p-layer 61. An insulation groove 9 is formedthrough the contact layer 62, the p-layer 61 and the emission layer 5.

[0065] The LED 10 in this example has a sapphire substrate 1 upon whichthe following five layers are consecutively formed: an AlN buffer layer2; a Si-doped GaN n⁺-layer 4 of high carrier (n-type) concentration; aZn and Si-doped GaN emission layer 5, Mg-doped Al_(0.1)Ga_(0.9)N p-layer61, and Mg-doped GaN contact layer 62. The AlN layer 2 has a 500 Åthickness. The GaN n⁺-layer 4 has about a 4.0 μm thickness and a2×10¹⁸/cm³ electron concentration. The emission layer 5 has about a 0.5μm thickness. The p-layer 61 has about a 0.5 μm thickness and a2×10¹⁷/cm³ hole concentration. The contact layer 62 has about a 0.5 μmthickness and a 2×10¹⁷/cm³ hole concentration. Nickel electrodes 7 and 8are formed to connect to the contact layer 62 and the n⁺-layer 4 of highcarrier concentration, respectively. The two electrodes are electricallyinsulated by a groove 9.

[0066] Here is explained a manufacturing process of the LED 10. Thesapphire substrate 1 and the AlN buffer layer 2 were prepared by thesame process described in detail in Example 1. On the AlN buffer layer2, about a 4.0 μm thick Si-doped GaN n⁺-layer 4 of high carrierconcentration with an electron concentration of 2×10¹⁸/cm³ was formedunder conditions of lowering the temperature in the chamber to 1150° C.,keeping the temperature constant and supplying N₂, NH₃, TMG, and dilutedsilane to 0.86 ppm by H₂ for 60 min. at a flow rate of 20 liter/min., 10liter/min., 1.7×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min.,and 10×10⁻⁹ mol/min., respectively.

[0067] The following manufacturing process and composition ratio providefor the three layers, the emission layer 5 as an active layer, thep-layer 62 as a clad layer, and the contact layer 62. The LED isdesigned to have 430 nm wavelength at peak in the luminous spectrum andhave luminous centers of Zn and Si.

[0068] About a 0.5 μm thick Zn- and Si-doped GaN emission layer 5 wasformed on the n⁺-layer 4 under conditions of lowering the temperature inthe chamber to 1000° C., keeping it constant and supplying N₂ or H₂,NH₃, TMG, DMZ, and diluted silane to 0.86 ppm by H₂ for 8 min. at a flowrate of 20 liter/min., 10 liter/min., 1.53×10⁻⁴ mol/min., 2×10⁻⁷mol/min., and 10×10⁻⁹ mol/min., respectively.

[0069] About a 0.5 μm thick Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 wasformed on the emission layer 5 under conditions of lowering thetemperature in the chamber to 1000° C., keeping the temperature constantand supplying N₂ or H₂, NH₃, TMG, TMA, and CP₂Mg for 7 min. at a flowrate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴mol/min., and 2×10⁻⁷ mol/min., respectively. At this stage, the p-layer61 remained insulative with a resistivity of 10⁸Ω·cm or more. Theimpurity concentration of the Mg-doped into the p-layer 61 was1×10¹⁹/cm³.

[0070] Then, about a 0.5 μm thick Mg-doped GaN contact layer 62 wasformed on the p-layer 61 under conditions of lowering the temperature inthe chamber to 1000° C., keeping the temperature constant and supplyingN₂ or H₂, NH₃, TMG, and CP₂Mg for 10 min. at a flow rate of 20liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., and 2×10⁻⁴ mol/min.,respectively. At this stage, the Mg-doped contact layer 62 remainedinsulative with a resistivity of 10⁸ Ω·cm or more. The impurityconcentration of the Mg-doped into the contact layer 62 was 1×10²⁰/cm³.

[0071] Then, the p-layer 61 and contact layer 62 were uniformlyirradiated by an electron beam under the same conditions as described inExample 1. Consequently, the p-layer 61 and contact layer 62 areprocessed to exhibit p-type conduction with a 2×10¹⁷/cm³ holeconcentration and 2 Ω·cm or more resistivity. The subsequent processsteps of forming the electrodes is the same as that described in theprevious example. As a result, the LED 10 having a singlehetero-junction structure is obtained whose emission layer is doped withZn as an acceptor and Si as a donor impurity. Alternatively, doping Mgand irradiating electrons into the emission layer 5 can be used toobtain an emission layer 5 with p-type conduction.

EXAMPLE 5

[0072]FIG. 11 shows a LED 10 embodied in this example. Three layers, ap-layer 61, an emission layer 5, and an n⁺-layer 4, are unique toExample 5. The p-layer 61 is formed of Mg-doped Al_(x1)Ga_(1-x1)N. Theemission layer 5 is Zn- and Si-doped Al_(x2)Ga_(1-x2)N. The n⁺-layer 4of high carrier concentration is Si-doped Al_(x3)Ga_(1-x3)N. Otherlayers and electrodes are formed the same as those described in Example4. The composition ratio of x1, x2 and x3 in each layer is designed tomake the band gap of the emission layer 5 smaller than those of then⁺-layer 4 and p-layer 61 forming a double hetero-junction structure ora single hetero-junction structure. Thanks to this structure, carriersare confined in the emission layer 5 contributing to higher luminousintensity. The emission layer 5 can exhibit any one of semi-insulative,p-type conductivity; or n-type conductivity.

EXAMPLE 6

[0073]FIG. 12 shows a LED 10 embodied in this example. Three layers, ap-layer 61, an emission layer 5, and an n⁺-layer 4, are unique toExample 6. The p-layer 61 formed of Mg-doped Al_(x1)Ga_(1-x1)N. Theemission layer 5 is formed of Zn- and Si-doped Ga_(y)I_(1-y)N. Then⁺-layer 4 of high carrier concentration is formed of Si-dopedAl_(x2)Ga_(1-x2)N. Other layers and electrodes are formed the same asthose described in Example 4. The composition ratio of x1, x2, and x3 ineach layer is designed to make the band gap of the emission layer 5smaller than those of the n⁺-layer 4 and p-layer 61 forming a doublehetero-junction structure or a single hetero-junction structure. Thanksto this structure, carriers are confined in the emission layer 5contributing to higher luminous intensity. The emission layer 5 canexhibit any one of semi-insulative, p-type conductivity, or n-typeconductivity.

[0074] The LED 10 in this example has a sapphire substrate 1 which hasthe following five layers are consecutively formed thereon: an AlNbuffer layer 2; a Si-doped Al_(x2)Ga_(1-x2)N n⁺-layer 4 of high carrier(n-type) concentration; a Zn- and Si-doped Ga_(0.94)In_(0.06)N emissionlayer 5, Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 of p-type, and anMg-doped GaN contact layer 62 of p-type. The AlN layer 2 has a 500 Åthickness. The Al_(x2)Ga_(1-x2)N n⁺-layer 4 has about a 4.0 μm thicknessand a 2×10¹⁸/cm³ electron concentration. The emission layer 5 has about0.5 μm thickness. The p-layer 61 has about a 0.5 μm thickness and a2×10¹⁷/cm³ hole concentration. The contact layer 62 has about a 0.5 μmthickness and a 2×10¹⁷/cm³ hole concentration. Nickel electrodes 7 and 8are formed to connect to the contact layer 62 and n⁺-layer 4 of highcarrier concentration, respectively. The two electrodes are electricallyinsulated by a groove 9.

[0075] A manufacturing process for the LED 10 of FIG. 12 is as follows.The sapphire substrate 1 and the AlN buffer layer 2 were prepared by thesame process described in detail in Example 1. On the AlN buffer layer2, about a 4.0 μm thick Si-doped Al_(x2)Ga_(1-x2)N n⁺-layer 4 of highcarrier concentration with an electron concentration of 2×10¹⁸/cm³ wasformed under conditions of lowering the temperature in the chamber to1150° C., keeping it constant, and supplying N₂, NH₃, TMG, TMA, anddiluted silane to 0.86 ppm by H₂ for 60 min. at a flow rate of 20liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., and10×10⁻⁹ mol/min., respectively.

[0076] Following manufacturing process and composition ratio for thethree layers, the emission layer 5 as an active layer, the p-layer 61 asa clad layer, and the contact layer 62, show an example where the LED 10is designed to have 450 nm wavelength at peak in luminous spectrum andhave luminous centers of Zn and Si.

[0077] About a 0.5 μm thick Zn- and Si-doped Ga_(0.94)In_(0.06)Nemission layer 5 was formed on the n⁺-layer 4 under conditions ofraising the temperature in the chamber to 850° C., keeping it constant,and supplying N₂ or H₂, NH₃, TMG, TMI, DMZ and, silane for 60 min. at aflow rate of 20 liter/min., 10 liter/min., 1.53×10⁻⁴ mol/min., 0.02×10⁻⁴mol/min., 2×10⁻⁷ mol/min., and 10×10⁻⁹ mol/min., respectively.

[0078] About a 0.5 μm thick Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 wasformed on the emission layer 5 under conditions of raising thetemperature in the chamber to 1000° C., keeping the temperature constantand supplying N₂ or H₂, NH₃, TMG, TMA, and CP₂Mg for 7 min. at a flowrate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴mol/min., and 2×10⁻⁷ mol/min., respectively. At this stage, the p-layer61 remained insulative with a resistivity of 10 ⁸ Ω·cm or more. Theimpurity concentration of the Mg doped into the p-layer 61 was1×10¹⁹/cm³.

[0079] Then, about a 0.5 μm thick Mg-doped GaN contact layer 62 wasformed on the p-layer 61 under conditions of keeping the temperature inthe chamber at 1000° C. and supplying N₂ or H₂₁ NH₃, TMG, and CP₂Mg for10 min. at a flow rate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴mol/min., and 2×10⁻⁴ mol/min., respectively. At this stage, the Mg-dopedcontact layer 62 remained insulative with a resistivity of 10 ⁸ Ω·cm ormore. The impurity concentration of the Mg doped into the contact layer62 was 1×10²⁰/cm³.

[0080] Then, the p-layer 61 and contact layer 62 were uniformlyirradiated by an electron beam with the same conditions described inExample 1. Consequently, the p-layer 61 and contact layer 62 areprocessed to exhibit p-type conduction with a 2×10¹⁷/cm³ holeconcentration and a 2 Ω·cm resistivity. The subsequent process steps offorming the electrodes is the same as that described in the previousexample.

[0081] In Examples 1 to 6, the emission layer 5 can exhibit any one ofsemi-insulation, p-type conductivity, or n-type conductivity. When theconcentration of the Zn-doped to the emission layer 5 is higher thanthat of the Si, the layer 5 exhibits semi-insulative characteristics.When the concentration of the Zn is smaller than that of the Si, theemission layer 5 exhibits n-type conduction.

[0082] In order to improve the luminous intensity, the impurityconcentration of Zn and Si doped to the emission layer 5 is preferablyin the 1×10¹⁷/cm³ to 1×10²⁰/cm³ range, respectively. The concentrationis more preferably in the 1×10¹⁸/cm³ to 1×10¹⁹/cm³ range. It is notpreferable that the impurity concentration be lower than 1×10¹⁸/cm³,because the luminous intensity of the LED decreases as a result. It isnot desirable that the impurity concentration is higher than 1×10¹⁹/cm³,because poor crystallinity occurs. It is preferable that theconcentration of Si is ten to one-tenth as that of Zn. The mostpreferable concentration of Si is in the one to one-tenth range orcloser to one-tenth to Zn.

[0083] In Examples 1 to 6, Cd, Zn, and Mg were employed as acceptorimpurities and Si as a donor impurity. Alternatively, beryllium (Be) andmercury (Hg) can be used as an acceptor impurity. Alternatively, carbon(C), germanium (Ge), tin (Sn), lead (Pb), sulfur (S), selenium (Se), andtellurium (Te) can be used as a donor impurity.

[0084] Electron irradiation was used in Examples 1 to 6 in order toprocess an emission layer 5 to exhibit p-type conduction. Alternatively,annealing, heat processing in the atmosphere of N₂ plasma gas and laserirradiation can be used.

EXAMPLE 7

[0085]FIG. 14 shows a structural view of a LED 10 embodied in Example 7.The LED 10 in this example was manufactured by additionally doping Mg tothe emission layer 5 of the LED 10 in Example 1. Other layers andelectrodes were manufactured the same way as those described in Example1.

[0086] CP₂Mg was fed at a flow rate of 2×10⁻⁷ mol/min. into a chamber inaddition to gasses employed in Example 1 in order to manufacture theemission layer 5 in Example 7. The emission layer 5 was about a 0.5 μmthick including Mg-, Cd-, and Si-doped(Al_(0.09)Ga_(0.91))_(0.99)In_(0.01)N remaining high insulative.Impurity concentration of the Mg, Cd and Si was 1×10²⁰/cm³, 5×10¹⁸/cm³,and 1×10¹⁸/cm³, respectively.

[0087] Then, electron beam was uniformly irradiated on both of theemission layer 5 and p-layer 6 with an electron diffraction device underthe same conditions as in Example 1. The emission layer 5 and p-layer 6came to exhibit p-type conduction with a hole concentration of2×10¹⁷/cm³ and a resistivity of 2 Ω·cm.

EXAMPLE 8

[0088]FIGS. 15 and 16 show structural views of a LED 10 embodied inExample 8. The LED 10 in this example was manufactured by additionallydoping Mg and irradiating electrons into the emission layer 5 of the LED10 in Example 6. The emission layer 5 of Example 8 includes Mg-, Zn-,and Si-doped Ga_(y)In_(1-y)N exhibiting p-type conduction. Other layersand electrodes were manufactured the same way as those described inExample 1.

[0089]FIG. 16 shows an example where the LED 10 is designed to have a450 nm wavelength at peak in the luminous intensity. The manufacturingprocess and composition equation of the three layers, the emission layer5 as an active layer, the p-layer 61 as a clad layer and the contactlayer 62 are described hereinafter.

[0090] The CP₂Mg was fed at a flow rate of 2×10⁻⁴ mol/min. into achamber in addition to gasses employed in Example 6 in order tomanufacture the emission layer 5 in Example 8. The emission layer 5 wasabout a 0.5 μm thick including Mg-, Zn-, and Si-dopedGa_(0.94)In_(0.06)N remaining highly insulative.

[0091] Then, the emission layer 5, p-layer 61 and contact layer 61 wereuniformly irradiated by an electron diffraction device under the sameconditions as those described in Example 1. This irradiation changed theemission layer 5, p-layer 61, and contact layer 62 into layersexhibiting p-type conduction with a hole concentration of 2×10¹⁷/cm³ anda resistivity of 2 Ω·cm.

[0092] In Examples 7 and 8, the impurity concentration of Zn and Sidoped into the emission layer 5 are preferably in the 1×10¹⁷/cm³ to1×20²⁰/cm³ range, respectively. The concentration is more preferably inthe 1×10¹⁸/cm³ to 1×10¹⁹/cm³ range. It is not preferable that theimpurity concentration be lower than 1×10¹⁸/cm³, because luminousintensity of the LED decreases as a result. It is not desirable that theimpurity concentration be higher than 1×10¹⁹/cm³, because poorcrystallinity occurs. It is further preferable that the concentration ofSi be ten to one-tenth as same as that of Zn. The most preferableconcentration of Si is in the two to one-tenth range.

[0093] In Examples 7 and 8, Cd, Zn and Mg were employed as acceptorimpurities and Si as a donor impurity. Alternatively, beryllium (Be) andmercury (Hg) can be used as an acceptor impurity. Alternatively, carbon(C), germanium (Ge), tin (Sn), lead (Pb), sulfur (S), selenium (Se) andtellurium (Te) can be used as a donor impurity.

[0094] Electron irradiation was used in Examples 7 and 8 in order tochange layers to have p-type conduction. Alternatively, annealing, heatprocess in the atmosphere of N₂ plasma gas, laser irradiation and anycombination thereof can be used.

[0095] While the invention has been described in connection with whatare presently considered to be the most practical and preferredembodiments, it is to be understood that the invention is not to belimited to the disclosed embodiments, but on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the spirit and scope of the appended claims.

What is claimed is:
 1. A light-emitting semiconductor device comprising: an n-layer with n-type conduction of group III nitride compound semiconductor satisfying the formula Al_(x3)Ga_(y3)In_(1-x3-y3)N, inclusive of x3=0, y3=0 and x3=y3=0; a p-layer with p-type conduction of group III nitride compound semiconductor satisfying the formula Al_(x1)Ga_(y1)In_(1-x1-y1)N inclusive of x1=0, y1=0 and x1=y1=0; an emission layer of group III nitride compound semiconductor satisfying the formula Al_(x2)Ga_(y2)In_(1-x2-y2)N, inclusive of x2=0, y2=0 and x2=y2=0; a junction structure of said n-layer, said p-layer, and said emission layer being any one of a homo-junction structure, a single hetero-junction structure, and a double hetero-junction structure; and wherein said emission layer is formed between said n-layer and said p-layer, and doped with both a donor and an acceptor impurity.
 2. A light-emitting semiconductor device of claim 1 , wherein said donor impurity is one of the group IV elements and said acceptor impurity is one of the group II elements.
 3. A light-emitting semiconductor device of claim 2 , wherein said donor impurity is silicon (Si) and said acceptor impurity is cadmium (Cd).
 4. A light-emitting semiconductor device of claim 2 , wherein said donor impurity is silicon (Si) and said acceptor impurity is zinc (Zn).
 5. A light-emitting semiconductor device of claim 2 , wherein said donor impurity is silicon (Si) and said acceptor impurity is magnesium (Mg).
 6. A light-emitting semiconductor device of claim 1 , wherein said emission layer exhibits any one of n-type conduction, semi-insulative and p-type conduction characteristics depending on concentration ratio of said donor impurity and said acceptor impurity doped thereto.
 7. A light-emitting semiconductor device of claim 1 , wherein said donor impurity is one of the group VI elements.
 8. A light-emitting semiconductor device of claim 1 , wherein the composition ratio of Al, Ga and In in said n-layer, said p-layer and said emission layer is designed to meet each of the lattice constants of said layers to a lattice constant of an n⁺-layer of high carrier concentration.
 9. A light-emitting semiconductor device comprising: an n-layer with n-type conduction of group III nitride compound semiconductor satisfying the formula Al_(x3)Ga_(y3)In_(1-x3-y3)N, inclusive of x3=0, y3=0 and x3=y3=0; a p-layer with p-type conduction of group III nitride compound semiconductor satisfying the formula Al_(x1)Ga_(y3)In_(1-x2-y1)N, inclusive of x1=0, y1=0 and x1=y1=0; an emission layer with p-type conduction of group III nitride compound semiconductor satisfying the formula Al Ga In, N, inclusive of x2=0, y2=0 and x2=y2=0 sandwiched between said n-layer and said p-layer; and wherein said emission layer has a narrower band gap than those of said n-layer and said p-layer, and has p-type conduction.
 10. A light-emitting semiconductor device of claim 9 , wherein said emission layer is doped with magnesium (Mg), a donor impurity, and an acceptor impurity.
 11. A light-emitting semiconductor device of claim 10 , wherein said donor impurity is one of the group IV elements and said acceptor impurity is one of the group II elements.
 12. A light-emitting semiconductor device of claim 11 , wherein said donor impurity is silicon (Si) and said acceptor impurity is cadmium (Cd).
 13. A light-emitting semiconductor device of claim 11 , wherein said donor impurity is silicon (Si) and said acceptor impurity is zinc (Zn).
 14. A light-emitting semiconductor device of claim 11 , wherein said donor impurity is silicon (Si) and said acceptor impurity is magnesium (Mg).
 15. A light-emitting semiconductor device of claim 11 , wherein the composition ratio of Al, Ga, and In in said p-layer, said n-layer, and said emission layer is designed to meet each of the lattice constants of said layers to a lattice constant of an n⁺-layer of high carrier concentration. 